Process of and apparatus for electroplating hollow parts



E. WORTH March 31, 1931.

PROCESS OF AND APPARATUS FOR ELECTROPLATING HOLLOW. PARTS Filed Dec. 20, 1928 Patented Mar. 31, 1931 PATENT ormcs ERNST WTTR'I'H, OF GOPPINGE'K GERMANY PROCESS OF AND APPARATUS FOR ELECTROPLA'IING HOLLOW ZPARTS Applicathnfiled December 20, 1928, Serial No. 327,264, and in Germany August 5, 1927.

My invention relates to the art of electro-- plating hollow shapes and more especially bars and the like of U-, C- or similar cross section. It is an object of my invention to eliminate certain difficulties encountered in the process of electroplating such parts. To this end I insert in the hollow shape to be treated a piece or strip of the metal to be deposited in such position that it partly pro- 1 jects into the hollow and partly projects therefrom. I then immerse the bar with the strip therein in a cell containing an'ele'ctrolyte in which an anode or a plurality of anodes is arranged, and connect the bar as the cathode. The problem of obtaining by electrodeposition metal-layers 'of uniform thickness on the inside of hollow shapes, for instance on the inside of bars of channel, C or other section,

the interior of which is accessible through a narrow slot, involves considerable difiiculties, the narrow opening interfering with the depth dispersion toward the inner surfaces and rendering it very unequal.

It has already been proposed to provide in such bars an inner anode but the insertion and insulation of such an anode is difficult as the anode must be practically equidistant from the inner faces of the bar, and this can only be obtained by providing exactly spaced insulating means which must be inserted through the narrow slot. But even if the operator succeeds in fixing up the anode satisfactorily, still the process involves difiiculties as the inner and outer layers must be deposited in separate stages-and it is necessary to perform each stage at a different voltage on account of the difference of distance between the inner and outer anodes on one side and the bar which is connected as the cathode on the other. The necessity of operating with different voltages involves extra cost as it is necessary to provide a separate machine for each voltage or to provide voltage regulating devices, resistances or the like.

It has also been suggested to use an electrolyte of such composition that the dispersion sufiices for depositing a layer on the inside as well as on the outside of the bar. This expedient dispenses with the necessity of providing extra equipment but it is not satisfactory as the layer on the inner faces becomes much thinner than the outside layer, and in order to obtain a layer of suitable thickness inside it would be necessary to deposit a layer of undue thickness outside. The necessity of depositing on the outer faces a layer which is thicker than required involves extra cost for current, metal and labour. Extra labour is required particularly in the case of outer layers which tend to grow on attaining a given thickness and to form bumps which must be removed by lifting the bars out of the cell and removing such irregularities by brushing.

Another drawback of the process just referred to is the necessity of placing the bars in such position that their slot faces one of the anodes, as bubbles which form in the electrolyte cannot escape from the bar on account of this position of the slot and where they form or stick, the deposit will be punctured.

Where the bar consists of a metal having a higher solution pressure than the 'metal to be deposited, the solution pressure within the practically closed bar has the tendency to overcome the solution pressure of the electrolyte, and if'this occurs, the metal of the bar enters into solution, contaminating the electrolyte and, under certain conditions, rendering it altogether unserviceable.

All these drawbacks are overcome according to my invention according to which the bar is connected as the cathode and placed in the cell with its slot up, and a strip of the metal to be electrodeposited is inserted in the slot by means of insulating spacing blocks so that the strip partly extends into the section of the bar and partly into the electrol te outside the bar. The bar is arrange intermediate normal anodes and preferably the strip extends in parallel to such anodes.

The metal strip then acts as a bipolar element, the surface projecting beyond the bar becoming the cathode and the surface within the bar the anode. This results in the deposition of a layer on the inside of the bar which is much thicker and much more uniform than a layer obtained by mere dispersion through the slot.

' In the drawings aflixed to this specification and forming part thereof, an apparatus embodying my invention is illustrated diagrammatically by way of example.

In the drawings Fig. 1 is a transverse section on the line I I in Fig. 2,

Fig. 2 is a longitudinal section on the line IIII in Fig. l viewed from the right,

Figs. 3 and 4 are sections of the bar illustrating the reversing of the metal strip to make up for its change of cross-section.

Referring to the drawings, 2' is a cell containing an electrolyte, a is the cathode bar, Z) is a bracket suspended from the bar, 0 is the hollow bar of C-shaped cross-section secured on the bracket with its slotted side up, e is a strip of the metal to be deposited, f, f are wedge shaped spacing blocks of insulating material, such as ebonite or the like, and d, d are the anodes which are suspended from suitable anode bars 7c, The strip 6 is secured in the bar a by means of the wedges 7 so that its upper part 9 projects into the electrolyte and its lower part it intothe bar. lVith this arrangement not only the bar 0 but also the surface 9 of the strip 6 acts as the cathode with respect to the anodes d while the surface it within the bar 0 acts as the anode with respect to the bar 0 and metal is deposited on the inside of the bar.

This effect is to a certain extent a function of the voltage in the anodes d. If it is desirable to start the process ata highervoltage this is readily effected by connecting the strip e for a short time as the anode and breaking this connection later on.

Any bubbles which may form in the electrolyte, are free to escape from the bar 0 as its slotted side is up, and will not interfere with the uniformity of the deposit.

After a certain time the thickness of the strip e will increase where it projects into the electrolyte as shown in Fig. 3. The strip is now reversed as shown in Fig. 4 and in this manner is fully utilized before it becomes necessary to remelt or to reroll it. Preferably the strip is reversed when a fresh bar 0 is inserted.

Obviously my invention is not limited to bars having the channel section illustrated but may be used for electroplating bars and other shapes of any section and origin, such as rolled sections, die-cast sections and the like.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described for obvious modifications will occur to a person skilled in the art.

In the claims afiixed to this specification no selection of any particular modification of the invention is intended to the exclusion of other modifications thereof and the right to subsequently make claim to any modification not covered by these claims is expressly reserved.

I claim 1. The method of electroplating hollow longitudinally slotted shapes comprising immersing such shape in an electrolytic cell comprising an anode, connecting said part as the cathode, and securing in the slot of the shape, but out of electrical contact with same a piece of the metal to be deposited in such manner that such piece partly projects into the hollow of said shape and partly into said cell outside of said shape.

2. The method of electroplating hollow longitudinally slotted shapes comprising immersing such shape in an electrolytic cell comprising an anode with its slot up, conmeeting said part as the cathode, and securing in the slot of the shape, but out of electrical contact with same, a piece of the metal to be deposited in such manner that such piece partly projects into the hollow of said shape and partly into said cell outside of said shape.

3. The method of electroplating hollow slotted shapes comprising immersing such shape in an electrolytic cell comprising an anode, connecting said part as the cathode, securing in the slot of the shape, but out of electrical contact with same a piece of the metal to be deposited in such manner that such piece partly projects into the hollow of said shape and partly into said cell outside of said shape, and reversing the position of said metal piece, after its outer portion has increased in thickness, so that the thicker part now extends into the hollow of said shape.

4. An electrolytic apparatus for depositing metal comprising a'cell, an anode and a hollow longitudinally slotted shape in said cell, and a piece of the metal to be deposited inserted in the slot of said shape but out of electrical contact with same so that it partly projects into the hollow of said shape and partly into said cell.

5. An electrolytic apparatus for depositing metal comprising a cell, an anode and a hollow slotted shape in said cell, a spacer of insulating material inserted in the slot of said shape, and a piece of the metal to be deposited held by said spacer so that it partly projects into the hollow of said shape and partly into said cell.

In testimony whereof I affix my signature.

ERNST WURTH. 

